Search a 2D Matrix

class Solution {
public:
    bool searchMatrix(vector<vector<int> > &matrix, int target) 
    {
        int row = matrix.size();
        if (row == 0) return false;
        int col = matrix[0].size();
        
        int left = 0, right = row - 1;
        
        while(left <= right) // 第一次二分找到在right行
        {
            if (matrix[left][0] == target || matrix[right][0] == target)
                return true;
            else if (matrix[left][0] < target)
                left += 1;
            else if (matrix[right][0] > target)
                right -= 1;
        }
        if (right < 0) return false; // 这个判断不能少，否则会run time error  因为right可能是-1
        int l = 0, r = col - 1;
        while(l <= r) // 第二次在第right行中二分找知否有值
        {
            if (matrix[right][l] == target || matrix[right][r] == target)
                return true;
            else if (matrix[right][l] < target)
                l += 1;
            else if (matrix[right][r] > target)
                r -= 1;
        }
        return false;
    }
};